Part 63

DENDROICA NIGRESCENS (Townsend)

BLACK-THROATED GRAY WARBLER

PLATE 35

HABITS

The black-throated gray warbler is neatly dressed in gray-black and white, with only a tiny spot of bright yellow in front of the eye. Its breeding range extends from southern British Columbia, Nevada, northern Utah, and northwestern Colorado southward to northern Lower California, southern Arizona, and southern New Mexico. It spends the winter in Mexico.

As a summer resident it is common and sometimes abundant in western Washington, even at lower elevations where, Samuel F. Rathbun tells me, it "prefers a locality somewhat open, with a second growth of young conifers; this may occur in the rather heavy forest, if such condition exists there, or along the edge of the timber; the species is partial to this character of growth."

In southern Oregon, according to C. W. Bowles (1902), it seems to combine the habitat requirements of the eastern black-throated green and the prairie warbler. Like the former, it seeks tall trees, preferably conifers, well scattered and interspersed with bushes, since it nests in both. Like the prairie warbler, it chooses high dry places with dry ground underneath for its nest.

Farther south, the black-throated gray warbler seems to prefer growths of hardwood and underbrush for its summer haunts--oaks, scrub oak, pinyon, juniper, manzanita, and the like. Dr. Walter K. Fisher wrote to Dr. Chapman (1907) that, in California, "it lives in chaparral such as deer brush, wild lilac of various species, scrub oak, and sometimes, particularly in the humid coast districts, among evergreens. It is fond of the neighborhood of clearings where it works constantly and carefully among low growth." Dr. Grinnell (1908) says that in the San Bernardino Mountains, "this warbler appeared to be be confined exclusively to the golden oak belt during the breeding season." Referring to the Great Basin region, Dr. Linsdale (1938) writes: "The black-throated gray warbler was one of the few species adapted to occupy the piñon belt on the Toyabe Mountains. Not only did this bird tolerate conditions on dry slopes, but it was practically limited to them. The pairs were scattered far apart, but because this type of habitat takes up so much of the total area, this warbler must rank high among all the summer resident birds on the basis of numbers."

This warbler is a common breeding bird in the mountains of southern Arizona. In the brushy foothills and canyons of the Huachucas, we found it between 4,000 and 7,000 feet in altitude, in the oak belt about halfway up the canyons, principally among the scrub oaks and manzanita bushes. In New Mexico, according to Mrs. Bailey (1928), it is found in summer at slightly higher levels, 5,500 to 8,000 feet, in the oak and pinyon pine country.

Nesting.--In Washington, the black-throated gray warbler seems to nest in fir trees exclusively, at heights ranging from 7 or 8 feet up to 50 feet above the ground. Rathbun has sent me the data for seven nests, all in firs, at heights ranging from 7-1/2 to 35 feet; they were all on horizontal branches and from 4 to 10 feet out from the trunk. He describes in his notes a typical nesting site as follows: "From a distance I saw a fir tree the character of which, from my experience, was favored by this warbler as a nesting place. It was of considerable size, one of a number scattered along the edge of the forest, and had considerable undergrowth beneath. After a very careful examination I located the nest near the extremity of one of the large lower limbs, at a distance from the trunk of 9 feet and at a height above the ground of 23 feet. The nest was placed at the side of the limb and was securely attached at a point where grew several small twig-like branches." He says that this bird is very regular in its nesting date, the average date for fresh eggs is between June 3 and 8, and that the nest is always a neat one. He describes a typical nest as follows: "Plant fibers, dry grasses and a few very small weed-stalks were all neatly woven together to form the walls of the nest. The lining was a few feathers--two being those of the ruffed grouse, with others from sparrows, the quill of each being worked into the walls of the nest; next to this lining were soft and very fine plant fibers, with a few horsehairs."

C. W. Bowles (1902) mentions a nest in southern Oregon that "was six feet up in a manzanita bush in a patch of bushes of the same variety about three acres in extent." But he adds that--

the nests were from three feet and three inches to twenty-five feet from the ground, oaks seeming the favorite in southern Oregon and fir near Tacoma. The usual situation is in a small clump of leaves that is just large enough to almost completely conceal the nest, and yet so very small that a crow or jay would never think of anything being concealed in them. * * * The nests externally are about 3 × 2-3/4 inches and internally 1-3/4 × 1-3/4 inches in diameter and depth. They are composed externally of grass and weed-stalks, that must be several seasons old, (being bleached and very soft) moss and feathers; and lined with feathers (one had evidently been lined from a dead Stellar jay), horse, cow and rabbit hair or fur, and sometimes the very fine stems of the flowers of some kind of moss. The male has never been seen to assist either at nest-building or incubation.

In the Yosemite region, where Grinnell and Storer (1924) found the black-throated gray warbler in fair numbers among the golden oaks on the north walls of the Valley, they found a nest "placed 5 feet 6 inches above ground in a mountain lilac (Ceanothus integerrimus) bush against a main stem."

From southern California, James B. Dixon writes to me: "This bird breeds sparingly from 2,500 feet to the tops of our mountain ranges in San Diego, Riverside and San Bernardino Counties. During my observations since 1898, I have seen but five nests. One was in a live oak tree, two in manzanita bushes and two in golden oak saplings." A nest in Riverside County, at 5,500 feet elevation, was in "a scrub growth area which was well wooded with sapling golden oak and manzanita, buck thorn, and other sparsely growing bushes." The nest was "located 12 feet from the ground in a deep, vertical crotch of a golden oak sapling, and could be seen from only one angle, much like the nest of a gnatcatcher or wood pewee." Another nest was found "in the dense growth of a young manzanita bush. * * * The locations of the two nests were extremely different, one was carefully concealed in a comparatively bare oak sapling, and the other in the dense foliage of a rank-growing young manzanita bush."

In the Huachuca Mountains of Arizona, I found but one nest of the black-throated gray warbler. It was 5 feet up in the main crotch of a small oak growing on a steep slope on the side of a branch of Ramsey Canyon; the slope was sparsely covered with scrub oaks and other bushes, with a scattering of tall pines; the nest was so well concealed that I could not get a clear photograph of it. Howard (1899) found three nests in these mountains in upright forks of oak saplings, and says: "I found other nests, some placed in large white oaks and some in sycamores and have known the birds to build high up in pines." One of his nests from these mountains, in the Thayer collection, was found only 18 inches up in a young fir tree in a thicket; lying against the main stem, it was supported, surrounded, and well concealed by live twigs. Four other nests in this collection, were all taken in the Huachuca and Chiricahua mountains from oaks at heights ranging from 6 to 16 feet above ground. All much alike, their decidedly gray appearance makes them less visible among the gray branches. They are made of light gray, old, shredded stems of dead weeds and grasses, very fine gray plant fibers and a few dead leaves, bits of string, and thread, all firmly bound with spider's web and decorated with numerous bits of spider cocoons. They are lined with fine brown and white hairs and small, soft feathers.

In New Mexico, Jensen (1923) reports two nests in piñon pines; one was 3 feet and the other 5 feet above ground.

Eggs.--From 3 to 5 eggs, usually 4, constitute a full set for the black-throated gray warbler. These are ovate to short ovate and are only slightly glossy. The ground color is white or creamy white and is speckled, spotted, and sometimes blotched with "chestnut," "auburn," "bay," or "russet," occasionally with "mummy brown," with underlying spots of "light brownish drab," or "light vinaceous drab." The spots are usually concentrated at the large end, forming a loose wreath, with the drab markings frequently in the majority. Some eggs are only lightly speckled, while others are boldly marked. The measurements of 50 eggs average 16.5 by 12.5 millimeters; the eggs showing the four extremes measure =18.2= by 12.3, 18.1 by =13.1=, =14.6= by 12.9, and 16.2 by =11.6= millimeters (Harris).

Young.--The period of incubation does not seem to have been recorded for this warbler. It is probably performed by the female entirely, but both parents share in the feeding of the young. Information on this subject is scanty.

Plumages.--The young black-throated gray warbler in juvenal plumage shows the characters of the species more than do the young of other wood warblers; the black and white areas about the head and throat are strongly indicated in a duller pattern and there are two broad white bars tipping the median and greater wing coverts (see pl. 35); these markings are more subdued in the female than in the male, thus making a slight sexual difference. The back is brownish gray and the underparts grayish white, faintly streaked with black.

I have not been able to trace the postjuvenal molt, but it is perhaps less extensive than in most other warblers. In first winter plumage the young male is much like the adult male at that season, but it is more strongly washed with brown above and with yellowish beneath, the chin is white, the black throat is mottled with white, and the streaking above and below is duller and more obscured. The young female differs from the adult female in about the same way.

Apparently, the nuptial plumage is produced mainly by wear, or by a limited prenuptial molt. The postnuptial molt is evidently complete in late summer.

The adult winter plumages of both sexes differ but little from the spring plumages; in the male, the feathers of the upper parts and cheeks are margined with brownish gray and the throat with white, the sides are washed with brown and the black streaks are obscured; in the female, the plumage is tinged with brownish in the same way and the black streaks are obscured.

Food.--No extensive study of the food of the black-throated gray warbler seems to have been made. It is evidently mainly, if not wholly, insectivorous, for several observers have mentioned its zeal in foraging among the foliage of trees and bushes for insects, with a special fondness shown for oak worms and other green caterpillars. Bowles (1902) says that "it seems to prefer oak trees in the spring because of the small green caterpillars that are very numerous on them and which are devoured on all occasions. One female must have eaten nearly half its weight of them (from three-fourths to one and one-half inches long) while its nest was being taken." Mrs. Wheelock (1904) writes in the same vein: "In the spring these oaks are particularly infested with the green caterpillars, and the Warblers never seem to tire of devouring the pests. They lean way over to peer under every leaf, or reach up to the twigs overhead, never missing one. Twenty of these worms is an average meal for a Black-throated Gray Warbler, and the total for a day must reach into the hundreds."

Behavior.--The black-throated gray warbler is not one of the most active wood warblers except when it is busy feeding; even then it goes about it in a quiet, business-like manner, without much concern over the presence of humans. At other times, it is rather shy and retiring, difficult to follow, as it slips away silently in the thick underbrush, where it spends so much of its time. Its nest is difficult to find, for it is not only well concealed, but the bird is careful not to betray it; our usual method of following a bird to its nest was not very successful, as it was soon lost to sight while we were watching it.

Mr. Bowles (1902) writes of its behavior that an incubating female "passed the time eating caterpillars while the nest was being examined. She did not go over five feet from it this time, till I left when she followed for about twenty feet, and kept almost within reach, watching me very closely. * * * Black-throated gray warblers do not object to human association at all; one nest was fifteen feet up on an oak branch, directly over a trail that was used at least six times a day by people going for mail, and generally much oftener."

William L. Finley (1904a) describes quite different behavior at a nest containing young: "The moment the mother returned and found me at the nest she was scared almost out of her senses. She fell from the top of the tree in a fluttering fit. She caught quivering on the limb a foot from my hand. But unable to hold on, she slipped through the branches and clutched my shoe. I never saw such an exaggerated case of the chills. I stooped to see what ailed her. She wavered like an autumn leaf to the ground. I leaped down, but she had limped under a bush and suddenly got well. Of course I knew she was tricking me! But I never saw higher skill in a feathered artist."

Voice.--The simple, but pleasing song of the black-throated gray warbler is described in Rathbun's notes as follows: "The song as ordinarily sung consists of three rather quickly given notes, of a somewhat lisping quality, that rise and fall but are alike in construction and a closing fourth note that may slur upward with a decided accent, or may fall. The real construction of this song is lost unless the singer is close by, for then it will be found that each of the first three notes is a double one. It is a clear and pleasing song, of good carrying quality, and somewhat smooth when heard at a distance. During the nesting season the males will be heard in song much of the time during the day. The habit of the bird is to perch on or near the top of a young evergreen tree and sing repeatedly without shifting its perch, then to fly to another tree of similar character and repeat its actions."

As I heard it in Washington, I wrote it swee, swee, ker-swee, sick, or swee, swee, swee, per-swee-ee, sic. Dr. Walter P. Taylor writes it in his notes zee zeegle, zeegle, zeegle, zort, tseeee. Grinnell and Storer (1924) describe it as "a rather lazy, drawling utterance, deep-toned rather than shrill. W[=e][=e]-zy, w[=e][=e]-zy, w[=e][=e]-zy, w[=e][=e]-zy-weet; tsewey, tsewey, tsewey, tsewey-tsew; zu[=e][=e], zu[=e][=e], zu[=e][=e], soop; s[)i][)i]]-w[=e][=e]zy, w[=e][=e]zy we-tsú; ow[=e]z[=e]-w[=e]z[=e]-w[=e]z[=e]-w[=e]z[=e]-ch[=u]r, are syllabifications written by us at different times when individual birds were singing close at hand. There are modifications in the song; sometimes the terminal syllable is omitted and again only three of the two-syllabled notes are given. The ordinary call is a rather low, one-syllabled chit."